Reused Frying Oil Linked to Brain Damage: Animal Study

New research on rats suggests reusing deep-frying oils may increase oxidative stress, inflammation, and neurodegeneration risk.

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Your guilty pleasure for crispy fried foods may be putting your brain at risk.

A new study in rats suggests that repeatedly reusing the same oil for deep-frying could increase the risk of neurodegeneration and associated conditions such as Alzheimer’s or Parkinson’s disease.

The culprit?

Toxic compounds formed when oil is reheated to scorching temperatures seem to disrupt the delicate communication network linking the liver, gut, and brain—with potentially devastating neural effects passed on to offspring.

Frying Oil Guidelines at Odds With Neurodegenerative Risks

Many of our favorite foods, such as french fries and fried chicken, are deep-fried. While the U.S. Department of Agriculture (USDA) maintains that frying oil can be safely reused and stored for up to three months, food service companies recommend changing the oil at least twice a week. For fryers used less frequently, the oil must be changed once every couple of weeks.

However, reusing frying oil can significantly affect brain health, according to research findings presented in March at the annual meeting of the American Society for Biochemistry and Molecular Biology.

The effects of reused oil on the bidirectional communication network between the liver, gut, and brain increased neurodegeneration. This liver–gut–brain axis plays a crucial role in regulating many physiological functions, and its dysregulation has been associated with neurological disorders, including Alzheimer’s and Parkinson’s diseases, multiple sclerosis, and autism.

1st Study to Link Reused Frying Oil to Offspring Brain Damage

While deep-frying at high temperatures has been linked to metabolic issues, there has been little long-term research on the health impacts of consuming deep-fried oils, Kathiresan Shanmugam, an associate professor at the Central University of Tamilnadu in India and lead researcher, said in a statement. He noted that this study was the first to show prolonged consumption of deep-fried oils increases neurodegeneration in offspring.

Researchers divided female rats into five groups, each consuming a different diet for 30 days. One group ate standard rat chow, while the others ate standard chow supplemented with 0.1 milliliter of unheated sunflower oil, unheated sesame oil, reheated sunflower oil, or reheated sesame oil.

The findings showed that rats consuming reheated oils experienced increased oxidative stress, liver inflammation, and colon damage. This led to alterations in liver lipid metabolism and decreased transport of essential brain fatty acids, resulting in neurodegeneration in the rats and their offspring.

The research also found that rat offspring consuming reheated oils were more likely to experience neuronal damage than those in the control group.

The study highlighted that reused frying oil loses its natural antioxidants and health benefits and may contain harmful compounds such as trans fats and acrylamide, a chemical known to damage the nervous and reproductive systems.

The researchers recommend supplementation with omega-3 fatty acids and nutraceuticals such as curcumin and oryzanol, which could help reduce liver inflammation and neurodegeneration. However, they noted that further clinical studies on the adverse effects of fried foods, especially those made with reused oil, are needed.

Tips for Safe Deep-Frying

“With any unsaturated oil, including olive oil, heating it repeatedly to a high heat (say for deep-frying) will cause the oil to develop compounds that have been found to have carcinogenic properties when tested on rats,” Tracy G. Hoyt, a functional medicine specialist in Murrieta, California, and owner of Hoyt Integrative Health, told The Epoch Times.

For safety and quality, Mr. Hoyt recommends using fresh cooking oil each time for frying foods. However, he acknowledged that “if you deep-fry large amounts of food frequently, it is not always practical from an economic standpoint.”

In those cases, choosing oils with a high smoke point, preparing food to minimize oil contamination, and straining the oil to remove any leftover food particles may be a good option, he noted. With proper storage, he added, “you can reuse most oils.”

Used oil that has not been properly strained and stored after cooling can become infected with dangerous bacteria that feed on food particles left in the oil, Mr. Hoyt said. Unrefrigerated used oil can also enable the growth of Clostridium botulinum bacteria, which produce a deadly botulism toxin, he added.

The safest cooking oil for deep-frying is avocado oil due to its high smoke point, according to Mr. Hoyt. Refined coconut oil is another good option, with a higher smoke point of 400 degrees to 450 degrees Fahrenheit than virgin coconut oil’s 350-degree smoke point, he noted.

Seed Oils to Avoid

There are eight toxic industrial seed oils: canola, corn, cottonseed, soybean, sunflower, safflower, grapeseed, and rice bran, Ron Grisanti, a functional medicine expert with a Diplomate American Clinical Board of Nutrition certification, told The Epoch Times.

These oils are processed at extremely high temperatures to oxidize their fatty acids. “This creates byproducts that are harmful to your health,” Mr. Grisanti said.

Excessive consumption of omega-6 fatty acids found in these seed oils can also trigger the body to produce pro-inflammatory chemicals, he said.

“When industrial seed oils are repeatedly heated, as restaurants do in fryers, even more toxic byproducts are created,” Mr. Grisanti said.